This invention relates to a multilayer tile, and a method of manufacturing the multilayer tile.
In general, tile is manufactured as follows: Feldspar, clay, and pottery stone are suitably pulverized and mixed. The mixture is further pulverized to form a mud-like material. The mud-like material thus formed is further pulverized to form a raw material for manufacturing tiles (hereinafter referred to as "tile raw material" or "tile-material") The tile-material is put in a mold and dry-pressed to form a molding. The molding is dried and then fired to obtain the desired tile.
A conventional tile manufacturing method is a so-called "one-layer molding method" in which one kind of tile-material is molded to form a molding for manufacturing a tile (hereinafter referred to as a "tile-molding") by pressing according to a tile-molding forming procedure as shown in diagrams (a) through (f) of FIG. 2. Diagrams (a) through (c) of FIG. 2 are sectional views, and diagrams (d) through (f) are top views. In the method, a mold consisting of a punch 1 and a die 2 as shown in the diagram (a) of FIG. 2 is employed. First, a tile-material supplying member 3 is moved as shown in diagrams (d) and (e) of FIG. 2 so that the tile-material 3a is placed in the cavity formed of the lower die 2a and side die 2b as shown in diagram (b) of FIG. 2. Thereafter, the tile-material supplying member 3 is returned to its original position as shown in diagram (f) of FIG. 2. Under this condition, the punch 1 is moved downwardly to press the tile-material in the die 2 to form a tile-molding as shown in diagram (c) of FIG. 2.
However, the one-layer tile manufactured according to the above-described one-layer molding method is disadvantageous in the following points:
(1) In order to color the molding, pigment must be distributed throughout the entire molding even though only the surface is desired to be colored. Therefore, the pigment is uneconomically used, with the result that the material cost is much increased. PA1 (2) In the case where the tile-material contains a material such as an iron compound which is readily molten, it is liable to adhere to refractory members such as shelf boards and rollers during the firing operation. As a result, the manufactured tiles may have defects, or the refractory members may be deteriorated. PA1 (3) It is difficult to give the inside of the tile a different function. PA1 (1) A colored tile can be obtained by mixing the pigment only in the outer layer of tile-material. Therefore, the pigment can be used economically, and the material cost can be reduced as much. PA1 (2) If a tile-material showing required color, surface quality, etc., is used for the outer layer of a tile to be manufactured, then a tile-material such as waste clay which is lower in quality can be used for the inner layer of the tile, which contributes to a reduction of the tile manufacturing cost. PA1 (3) Even in the case where tile-material having the desired quality contains a material such as an iron compound which is liable to be molten during the firing operation, the above-described disadvantages can be eliminated as follows: If a tile-material which does not contain such a material is used for forming the under layer of the tile, then the difficulty that the molding adheres to the refractory members during firing is eliminated. Accordingly, the aforementioned problems that the manufactured tiles are defective and the refractory members are deteriorated are eliminated. PA1 (4) Materials such as non-plastic materials which cannot be molded without other additional materials can be employed to form a tile-molding. That is, in the two-layer molding method, a tile-molding can be formed by combining the tile-material with a material which is high in strength.
In order to overcome these disadvantages, recently a two-layer molding method has been employed in which, as shown in diagrams (a) through (e) of FIG. 3, two kinds of tile-material are placed in the die and pressed to form a tile-molding. Diagrams (a) through (e) of FIG. 3 are sectional views and diagrams (f) through (j) are top views. In the method, a punch 1, a die 2, and two tile-material supplying members 3 and 4 are used. First, one 3a of the two kinds of tile-materials is placed in the die 2 with the tile-material supplying member 3 as shown in diagrams (b), (g), and (h) of FIG. 3, and then the lower die 2 is lowered as shown in diagram (c) of FIG. 3. Under this condition, the other tile-material 4a is placed in the cavity of the die 2 with the other tile-material supplying member 4 as shown in diagrams (i), (d), and (j) of FIG. 3. Thereafter, the punch 1 is moved downwardly to press the tile-materials laid in two layers to form a two-layer molding as shown in diagram (e) of FIG. 3.
The above-described two-layer molding method is advantageous in the following points:
The two-layer molding method is advantageous as described above; however, it is still disadvantageous in the following points:
In the manufacture of a two-layer tile, the upper layer of tile-material and the lower layer of tile-material differ in the degree of shrinkage while the tile is drying and firing. That is, in such case, the degree of shrinkage therebetween becomes clearly different in the steps of the firing as the temperature increases and the maturing. In the other case that the tile material is already fired, the upper layer of fired tile-material and the lower layer of fired tile-material becomes different in contraction while the tile is cooling. That is, the contraction corresponds with the thermal expansion coefficient. Therefore, the expansion between the upper layer of fired material and the lower layer of fired material becomes clearly different after the firing temperature over a peak thereof. Then, the tile-molding is deformed, or bent. As the tile-molding is further deformed, the upper layer of tile-material and the lower layer of tile-material become partially or totally separated from each other.
If the upper layer of tile-material and the lower layer of tile-material are equal to each other in thermal expansion coefficient or shrinkage, the above problem would not occur. However, in general, the upper layer of tile-material is much different in thermal expansion coefficient or shrinkage from the lower layer of tile-material, and therefore the difficulty that the two-layer tile is bent during the firing operating cannot be eliminated. This tendency is significant especially in a tile 300 mm.times.300 mm or larger.